1. Field of the Invention
This invention relates to compositions useful in defoaming aqueous mixtures, particularly pulp liquor.
2. Description of the Prior Art
It is known to prepare defoamer compositions for aqueous liquids which must contain both an oil-soluble and oil-insoluble, solid organic polymer from U.S. Pat. No. 3,793,223. In this patent there is disclosed the use of a copolymer of vinyl acetate and fumaric acid esterified with a tallow alcohol and containing excess vinyl acetate but there is no teaching that such a polymer is useful alone or in combination with a mineral oil as a defoamer. In U.S. Pat. No. 3,730,894, there is disclosed a process for inhibiting foaming in a liquid system containing water and a hydrocarbon utilizing as a defoamer a solid, particulate, insoluble material such as a copolymer of vinyl stearate and maleic anhydride but there is no indication that the alkyl esters thereof are useful as defoamers. Mineral oil compositions containing esterified copolymers of .alpha.-.beta.-unsaturated polybasic acids with vinyl ethers are disclosed in U.S. Pat. No. 2,704,277 as having lower pour points and improved viscosity indexes; such mineral oil compositions being useful as lubricants. Esterified copolymers of maleic anhydride and a vinyl ether are disclosed in U.S. Pat. No. 2,866,775 for use as pressure-sensitive adhesives.